Move NetHttpCoverageTest to external/cronet TEST_MAPPING

It seems that aosp/3086726 landed before aosp/2910846 and did not result
in any merge conflict which led to a leftover entry for cronet tests.

This CL removes it and in the same topic, it is moved to external/cronet

Bug: 338358650
Test: TH
Change-Id: If875f252aaadedff8d5ed520bdb152874b6fa9c3
diff --git a/TEST_MAPPING b/TEST_MAPPING
index 375397b..4cf93a8 100644
--- a/TEST_MAPPING
+++ b/TEST_MAPPING
@@ -77,18 +77,6 @@
       "name": "libnetworkstats_test"
     },
     {
-      "name": "NetHttpCoverageTests",
-      "options": [
-        {
-          "exclude-annotation": "com.android.testutils.SkipPresubmit"
-        },
-        {
-          // These sometimes take longer than 1 min which is the presubmit timeout
-          "exclude-annotation": "androidx.test.filters.LargeTest"
-        }
-      ]
-    },
-    {
       "name": "CtsTetheringTestLatestSdk",
       "options": [
         {